Command Section
SU(1)                   FreeBSD General Commands Manual                  SU(1)

     su - substitute user identity

     su [-] [-c class] [-flms] [login [args]]

     The su utility requests appropriate user credentials via PAM and switches
     to that user ID (the default user is the superuser).  A shell is then

     PAM is used to set the policy su(1) will use.  In particular, by default
     only users in the ``wheel'' group can switch to UID 0 (``root'').  This
     group requirement may be changed by modifying the ``pam_group'' section
     of /etc/pam.d/su.  See pam_group(8) for details on how to modify this

     By default, the environment is unmodified with the exception of USER,
     HOME, and SHELL.  HOME and SHELL are set to the target login's default
     values.  USER is set to the target login, unless the target login has a
     user ID of 0, in which case it is unmodified.  The invoked shell is the
     one belonging to the target login.  This is the traditional behavior of
     su.  Resource limits and session priority applicable to the original
     user's login class (see login.conf(5)) are also normally retained unless
     the target login has a user ID of 0.

     The options are as follows:

     -c class
             Use the settings of the specified login class.  The login class
             must be defined in login.conf(5).  Only allowed for the super-

     -f      If the invoked shell is csh(1), this option prevents it from
             reading the ``.cshrc'' file.

     -l      Simulate a full login.  The environment is discarded except for
             HOME, SHELL, PATH, TERM, and USER.  HOME and SHELL are modified
             as above.  USER is set to the target login.  PATH is set to
             ``/bin:/usr/bin''.  TERM is imported from your current
             environment.  Environment variables may be set or overridden from
             the login class capabilities database according to the class of
             the target login.  The invoked shell is the target login's, and
             su will change directory to the target login's home directory.
             Resource limits and session priority are modified to that for the
             target account's login class.

     -       (no letter) The same as -l.

     -m      Leave the environment unmodified.  The invoked shell is your
             login shell, and no directory changes are made.  As a security
             precaution, if the target user's shell is a non-standard shell
             (as defined by getusershell(3)) and the caller's real uid is non-
             zero, su will fail.

     -s      Set the MAC label to the user's default label as part of the user
             credential setup.  Setting the MAC label may fail if the MAC
             label of the invoking process is not sufficient to transition to
             the user's default MAC label.  If the label cannot be set, su
             will fail.

     The -l (or -) and -m options are mutually exclusive; the last one
     specified overrides any previous ones.

     If the optional args are provided on the command line, they are passed to
     the login shell of the target login.  Note that all command line
     arguments before the target login name are processed by su itself,
     everything after the target login name gets passed to the login shell.

     By default (unless the prompt is reset by a startup file) the super-user
     prompt is set to ``#'' to remind one of its awesome power.

     Environment variables used by su:

     HOME  Default home directory of real user ID unless modified as specified

     PATH  Default search path of real user ID unless modified as specified

     TERM  Provides terminal type which may be retained for the substituted
           user ID.

     USER  The user ID is always the effective ID (the target user ID) after
           an su unless the user ID is 0 (root).

     /etc/pam.d/su      PAM configuration for su.

     su -m man -c catman
            Starts a shell as user man, and runs the command catman.  You will
            be asked for man's password unless your real UID is 0.  Note that
            the -m option is required since user ``man'' does not have a valid
            shell by default.  In this example, -c is passed to the shell of
            the user ``man'', and is not interpreted as an argument to su.
     su -m man -c 'catman /usr/share/man /usr/local/man'
            Same as above, but the target command consists of more than a
            single word and hence is quoted for use with the -c option being
            passed to the shell.  (Most shells expect the argument to -c to be
            a single word).
     su -m -c staff man -c 'catman /usr/share/man /usr/local/man'
            Same as above, but the target command is run with the resource
            limits of the login class ``staff''.  Note: in this example, the
            first -c option applies to su while the second is an argument to
            the shell being invoked.
     su -l foo
            Simulate a login for user foo.
     su - foo
            Same as above.
     su -   Simulate a login for root.

     csh(1), sh(1), group(5), login.conf(5), passwd(5), environ(7),

     A su command appeared in Version 1 AT&T UNIX.

FreeBSD 11.1-RELEASE-p4         August 11, 2013        FreeBSD 11.1-RELEASE-p4
Command Section